In a rail train, states of apparatuses mounted on cars constituting the train are usually monitored by a monitoring device arranged at a head car, and a network is constructed to collect information of the apparatuses of the cars (see PTLs 1 and 2, for example).
When changing a train set of the rail train, the cars are combined or split. Therefore, typically, networks for the respective cars are constructed, and a network for the entire train set is constructed. Hereinafter, the network for each car is referred to as an “intra-car network”, and the network for the entire train set is referred to as an “inter-car network.”
When changing the train set (when combining or splitting the cars), the intra-car networks are connected to one another or disconnected from one another. Therefore, typically, the intra-car networks serve as local networks, the inter-car network serves as a global network, and these networks are connected to one another through routers.
Normally, a plurality of apparatuses mounted on the car are connected to the intra-car network for, for example, collecting apparatus information, such as an operation log. The apparatus information of all the cars in the train set can be confirmed by the monitoring device of the head car including a driver's seat. For example, when an operation abnormality of the apparatus occurs, it is informed to a driver. Examples of the apparatus information include information indicating operation states of doors, lighting apparatuses, and air conditioners, and information indicating abnormalities of doors, lighting apparatuses, and air conditioners.
When the monitoring device and each of a large number of apparatuses in the other cars communicate with each other to, for example, collect the apparatus information of all the cars, there is a problem that traffic of the inter-car network increases, and throughput of the inter-car network decreases. This problem becomes significant as the number of cars in the train set increases.
Further, when the monitoring device of the head car communicates with each of a large number of apparatuses in the other cars as described above, each router connecting the intra-car network and the inter-car network performs an address translation based on a table (NAT table) that records an address translation method regarding the respective apparatuses. However, when additions, changes, or the like of addresses are required due to, for example, an increase or decrease of the apparatuses, the NAT table needs to be suitably updated. Thus, there is a problem that a labor of managing the NAT table is required. Furthermore, a state where all the apparatuses are accessible from the other cars is not preferable in terms of security.
To avoid these problems, in many cases, monitoring devices each connected to the corresponding intra-car network for information collection are provided at the respective cars, the apparatus information of the cars are collected and processed by the respective monitoring devices, and the inter-car network is used only for communication among the monitoring devices. For example, when the apparatus of the car other than the head car is abnormal, abnormality information is transmitted from the monitoring device of the car through the inter-car network to the monitoring device of the head car. In this case, since the NAT table records only the address translation method regarding the monitoring devices, the labor of managing the NAT table can be reduced, and the deterioration of the security can be suppressed.